The fluxes and concentrations of materials from two contiguous second-order watersheds in the Coastal Plain of Maryland, U.S.A. were measured for six years prior to and six years subsequent to the formation of a 1.25 ha beaver pond near the bottom of one of the watersheds. The watersheds have a clay aquiclude and were equipped with V-notch weirs and continuous volume-integrating water samplers. The beaver pond reduced annual discharge of water, total-N, total-P, dissolved silicate, TOC, and TSS by 8, 18, 21, 32, 28, and 27%, respectively. Most of the total-N reduction was due to increased retention of nitrate in the winter and spring and TON in the winter and summer. Most of the total-P reduction was the result of retention of both TPi and TOP in the winter and summer. Dissolved silicate retention peaked in the spring, while TOC and TSS retention peaked in the winter. Prior to the formation of the beaver pond, concentrations of TON, TPi, TOP, TOC, and TSS had highly significant correlations with stream discharge, especially in the winter, but subsequent to the pond there was little or no relationship between these concentrations and stream discharge. However, concentrations of nitrate in the spring and ammonium in the summer were highly correlated with stream discharge both before and after the formation of the beaver pond and regressions of discharge versus concentrations of these nutrients explained more of the variation in concentrations after the formation of the pond.
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